There’s a reason fitness instructors always say these three things

One quick way to end a workout? Pass out. Fainting isn’t common at gyms, says Nick Clayton, personal training program manager for the National Strength and Conditioning Association, but he’s seen it happen. And in every case, it’s been because someone ignored a cardinal rule of exercise. Fitness instructors say lots of things that may or may not be true. (“You can do it,” for instance.) But there are commands they repeat that can’t be denied, unless you’d like to wind up with some very unwelcome consequences — and possibly collapsed in a heap on the floor.

Remember to Breathe

Depriving the body of oxygen forces the heart to pump harder. As Clayton explains: “You’re not necessarily out of shape. You’re not getting the air necessary.”

That’s why he emphasizes diaphragmatic breathing, particularly with stressed clients who tend to suck in gasps just to their neck and chest. (“If your collarbone rises and falls when you breathe, you’re likely a shallow breather,” Clayton says.)

D.C.-based trainer Lisa Reed keeps clients oxygenated by telling them to “inhale for five, exhale for five.” Repeating that mantra — and reminding them to exhale during the exertion phase of an exercise — drills proper technique, which helps them lift more and stretch farther.

Keep Drinking Water

“The moment you’re dehydrated, it’s a disaster. Technique just goes,” Reed says. Plus, water can stave off headaches, cramps and several scarier scenarios — including fainting.

Clayton encourages his clients to drink up before, during and after a workout. His trick for daily water consumption: He starts each morning by putting two rubber bands at the bottom of a 32-ounce water bottle, and fills it up. When he’s finished drinking what’s in there, he pushes one rubber band to the top and then repeats.

You can tell you’re getting enough liquid, Clayton notes, by examining your urine color. You want it light yellow — like lemonade — he says. “But I don’t want to see it,” he adds.

Stick Around for the Cooldown

You’ve got air. You’ve got water. Don’t stop now.

Really, don’t stop, begs Reed, who notes that shutting down rather than cooling down can make you fall down. When you’re pushing yourself hard during a workout, she explains, your blood pressure spikes. So cutting off your activity abruptly without letting your body return to normal is a risky proposition.

She insists all of her clients do something after intense exercise, whether it’s going for a light jog or pedaling a stationary bike.

Clayton has found that saying, “I want you to get on the bike for five minutes so you won’t have a heart attack” usually does the trick when clients protest.